Ask HN: Is it possible to sell you own excess on AWS?

What if you could reduce your hosting costs per CPU hour by selling off your own excess cycles from within your instance. What if you could purchase cycles at a lower cost than spot instances?

I'd bet there are many applications that have a number of reserve instances as part of their architecture that are mostly idle. Is it reasonable to assume they'd want to sell off some cycles if it wouldn't adversely affect their application? Is it reasonable to assume people would want to purchase cycles in this way? Ie, for doing things like moving data in and out of S3, those calls could be made from another instance that isn't yours at a cheaper cost - assuming security wouldnt be an issue.

Why isn't this available? Is it simply a security question?